Discharge device



- Aug. e, 1940.

L. D. MILES DISCHARGE DEVICE Filed Feb. 2, 1939 2 Sheets-Sheet 1 f s Z s Inventor Lawrence D. Miles,

y Attorney.

Aug. 6, 1940. l.. D. MILES DISCHARGE DEVICE FiledFeb. 2, 1939 2 Sheets-Sheet 2 Inventor* Lawrence D. Miles,v

I-Is Attorhey.

Patented Aug. 6, 1940 DISCHARGE DEVICE V Lawrence D. Miles, Ballston Lake, N. Y., assignor f ,i to General Electric Company., a corporation of vNew York Application February 2, 1939, Serial No. 254,156

6 Claims.

This application is a continuation-in-part of my prior application Serial No. 168,197, filed October 9, 1937.

The present invention relates to improvements in discharge devices which operate with an arclike discharge. While not limited thereto, it is primarily applicable in connection with devices which employ a self-reconstructing cathodev of extensive surface area. Such cathodes are best exemplified 'by the mercury pool and for that reason are referred to herein as pool type cathodes. It should be understood, however, that the term pool type cathode'as used herein and in the appended claims is not limited to liquid metals such as mercury, but is intended also to include solid substances which are capable of analogous use. Particular examples of such solid substances include cadmium and bismuth.

It is an object of the invention to provide means for confining the Acathode spot to a desired region of the cathode surface. Such operation is especially desirable, for example,`in connection with. a metal-enclosed discharge device in which it is necessary to prevent the cathode spot from reaching and becoming fixed to the envelope wall.

The object specified in the foregoing is attained in accordance with the present invention by the use of means for producing a magnetic field whichvacts on the cathode spot or on the arc i.) Ll

CII

itself in such a way as to limit the l'motion of the spot. i.

The features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself. together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the drawings in which Fig. 1 represents partly in section a discharge device suitably embodying the invention; Fig. 2 is a transverse Vsectional View taken on line 2-2 of Fig. 1;-Fig. 3 shows a modification of Fig. l.; Fig. 4 illustrates an alternative application of the invention; and Figs. 5. 6 and 7 are enlarged fragmentary sectional views showing in detail certain of the elements of Fig. 4.

Referring particularly to Fig. 1, there is shownv a discharge device comprising an enclosing envelope I0 constituted of metal. yThis comprises a main cylinder formingthe side Walls of the envelope and a pair of transverse headers II and I2 which respectively close the envelope ends.

At the upper end of the envelope there are provided a pair of anodes I3 and I 4 which are insulatingly supported from the envelope by means of glass-to-metallead-in seals I6 and II.

A 'barrier I9, interposed between the anodes, serves to separate their discharge paths and minimize the danger of arc-over between them.

At the lower end of the envelope and in col operative relation-with the anodes I3, I4 there is provided a pool-type cathode 2-I comprising a quantity of mercury in direct contact with the header II. A current connection to the cathode may be made by means of a heavy stud 22 attached tothe header. f

In order to initiate a discharge through the device, one may employ a make-alive electrode such as is indicated at 24. This may comprise, for1 example, a tapered rod of asemi-conducting material such as boron carbide having its tip immersed in the cathode material. A lead-in connection 25 (Fig. 2) permits a starting potential to be applied to this electrode to initiate a cathode spot at the cathode surface. After the discharge is once started in this manner, it can be maintained by the alternate energization of the anodes I3 and I4.

In a device of the type described, wherein the discharge is of arc-like character, the cathode terminal of the discharge comprises Aa so-called cathode spot. This comprises a concentrated luminous area which tends to'move rapidly over the cathode surface and which may under'certain conditions become attached to the wall of the discharge envelope, resulting in disintegration thereof. In order to `prevent this latter occur;- rence, it is desirable to confine the cathodaspot to a particular region of the `cathode surface. My present invention comprises a novel means by which this result may be effectively accomplished. l

In this connection there is, shown outside the envelope I0 a magnetic structure 28 having its respective poles in direct contact with the surface of the header Il. This magnet may be permanently magnetized or separately excited by a D. C. i'leld winding applied thereto. Within the envelope and cooperating with themagnet 28 there are provided auxiliary pole pieces 30 and 3| constituted of magnetic material. As shown, these project above the cathode surface and are effective to coniine the fiuxpassing between the poles of the magnet 28 mainly to a direction which is parallel to the'cathode surface that is to say, transverse to the normal discharge path'.

I have found that a magnetic field of this character, operating at the cathode terminal of an arc-like discharge, tends to control the motion of the cathode spot. Thisjs apparently accomplishedl by the action of the magnetic 'iield in exerting a positive force on the cathode spot or on the components of the arm directly associated therewith.

The resultant motion of the cathode spot is in a direction opposite from that which would be expected solely upon consideration of the reaction between the magnetic eld and the current stream flowing between the cathode 2| ,and either of the anodes I3 and |4. That is to say, assuming that thepole 30 of Fig. 1 is a north pole and the pole 3| a south pole, a cathode spot existing,y

between the poles is caused to move in a direction toward the observer. This is true in spite of the fact that the arc-stream itself tends to move away from the observer in accordance with the socalled left hand rule of electromagnetic reaction. I am not at the present time able to offer a complete explanation for this phenomenon, although I have frequently veried it in practice.

The action of the magnetic field above described obviously serves to prevent motion of the cathode spot in one direction only. In order completely to x the spot, therefore, it is necessary to provide means for restricting its motion in other directions. Such means may comprise, for example, a barrier such as is illustrated at v34 (Figs. 1 and 2). It is the function of this lbarrier partially to enclose the cathode spot and to prevent its motion in all directions except that which is prohibited by the action of the magnetic field.y In the particular form illustrated, which is to be taken as exemplary only, the barrier comprises a `V-shaped member which projects partly above and partly below the mercury surface. The apex ofthe angle formed .by the member points in the direction of the force exerted on the cathode spot by the magnetic field. Under these conditions, the cathode spot, when once established in the'vicinity of the barrier, tends to assume a position su'ch as is indicated at 36. With this arrangement, while increases in the discharge current may tend to increase the dimensions of the cathode spot, they will not, for

any normal condition, cause it to become dislodged from its connement to-a particular region of the cathode surface. The barrier 34 may be constituted of any suitable refractory material of conducting or insulating character. I prefer, however, to form it of a metal such as tungsten ormolybdenum which inherently exerts an anchoring action on a cathode spot in contact with it.

The magnetic structure may obviously assume many forms different from that shown in Fig. 1. In Fig. 3, for example, there is illustrated an alternative arrangement wherein the header Il is provided with reentrant pockets`38 and 39 adapted to receive the pole pieces of an externally arranged magnet '28. The operation of this structure is essentially similar to that of Fig. l.

In Fig. 4 I have illustrated the application of my invention in connection witha discharge device having means for producing a holding arc and further means for segregating the discharge space of the holding arc from the main body of the discharge envelope as described and claimed in my prior application Serial No. 168,197, above referred to. In this case there is provided a metal discharge envelope 40 which encloses only a single main anode 4| adapted to receive a discharge from a cooperating cathode 42. With this construction the discharge, once initiated, must be maintained by a separate keep-alive dev1ce.

In the arrangement illustrated the keep-,alive Vchannel 50.

means comprises a pair of auxiliary anodes 44 and 45 which are positioned above the surface of the cathode 42. As explained in my aforesaid prior application, it is desirable for certain uses to confine the discharge path of the holding arc so that it is substantially segregated from the main discharge chamber. In the present case this object is partiallyy accomplished by enclosing the anodes "44 and 45 in a shielding housing 41 which comprises an inverted cup-like member consisting, for example, of quartz. This 'housing does not extend quite to the cathode surface'but is provided with a metallic extension 48 (Fig. 5) consisting of molybdenum or a like refractory metal.

The crosssectional outline of this extension is illustrated in Fig. 6, which comprises a section taken on'line 6 6 of Fig. 5. From this figure it will be seen that the part 48 comprises a portion of generally cylindrical outline which has been distorted so as to include a reentrant portion 49 lforming a narrow slot or channel 50. In the operation oi' the device this channelis adapted to receivefand retain the cathode spot in the position. indicated at 5|. IThe restricted opening comprising `the mouth of the channel thus provides substantially the only connection between the discharge path of the holding arc and the main discharge chamber.

The purpose of an arrangement such as that described is to assure that the cathode spot shall be initiated aty the beginning of each current cycle at a point relatively close to the member 448 and remote from the metallic wall of the envelope 40. This is accomplished byV Virtue of the ,fact that the cathode spot of the holding arc tends tothe-'retained at all times within the Consequently, when the potential applied between the main anode 4| and the cathode 42 is favorable toa discharge, the cathode spot shown at 5| subdivides and creates another cathode spot corresponding to the main ldischarge arc ata point outside the slot 50 but in the vicinity of the shielded holding arc assembly. This latter cathode spot is extinguished at the endof each current cycle and is reestablished in approximately the same position at the beginning of the next current cycle. `It is free to wander over the cathode surface, but is prevented from becoming xed to the envelope wall by virtue of being cyclically recalled tothe vicinity of the-holding-arc assembly.

, VWhile the usual operation of the apparatus described is as explained in the foregoing, there is some tendency for the cathode spotv 5| to be drawn out of the slot 5|) and to be'extinguished. In .order to prevent -this possibility, use is made of the magnetic spot retaining means previously described in connection with Fig. 1. This may comprise, for example, a vpermanent magnet indicated at and having interior pole pieces 56 andY 5l which function 4to confine the magnetic ilux to the desired region. For proper operation with the` arrangement shown in Figs. 4 to 6, the pole 56 should be anorth pole and the pole 51 should be a south pole. Under these conditions the force exerted on the arc will be in such a direction as vcontinuously to impel the cathode spot 5|.into the slot or lchannel 50.

For `some uses it is desirable to control the initiation of the discharge; that is to say, to provide means for determining whether or not a discharge shall takeplace during any given cycle. This is accomplished in the present con- .neCtiQn br-,providing.adjacent the opening of `shielding means substantially segregating the the slot 50 an electrostatic control member or grid. In the arrangement shown, the grid cornprises a perforate body 58 consisting of a heatressting conductor of good radiating properties, for example, graphite. It is supported out of contact with the cathode 4-2 and may be supplied with a control potential by means of a suitable lead-in conductor (not shown in the drawings).

While I have described my invention in connection with particular structures, it will be understood that it may be employed with equal benet in any case where it is desired to confine the cathode spot to a particular region of the surface of a cathode of extended area. Numerous modifications may be made by those skilled in the art without departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations as fall Within the true spirit and scope of the foregoing description.

What yI claim as new and desire to secure by Letters Patent of the United States is:

1. A discharge device comprising an anode, a pool type cathode, a barrier for restricting the motion of the cathode spot on the cathode surface, and magnetic meansfor impelling the cathode spot against the said barrier, thereby to maintain the spot in substantially fixed position on the cathode surface.

2. A discharge device comprising an anode, a pool type cathode, a barrier extending above the cathode surface and providing a partial enclosure adapted to confine the cathode spot to a particular region of the cathode surface, and means for producing a substantially unidirectional magnetic leld parallel to the cathode surface in the vicinity of the barrier so as to prevent the cathode spot from leaving the said enclosure.

3. A discharge device comprising means forming a principal discharge space, means providing terminals for a discharge passing through said space, said terminal means including a pooltype cathode, one or more keep-alive electrodes cooperating with the cathode surface for maintaining a holding are adapted to facilitate the initiation of a discharge between said terminals,

holding arc from the main discharge space except for the provision of a restricted opening in the shielded means at the cathode surface, and means for producing a magnetic field acting transversely of the discharge path so as to prevent the holding arc cathode spot from leaving the said shielding means.

4. A discharge device comprising means forming a principal discharge space, means providing terminals for a discharge passing through said space, said terminal means including a pool-type cathode, one or more keep-alive electrodes cooperating with the cathode surface for maintaining a holding arc adapted to facilitate the initiation of a discharge between said terminals, and means for controlling the initiation of such a discharge, said last-named means including a shielding member substantially segregating the discharge space of the holding arc from theI principal discharge space except for the provision of a restricted passage between such spaces adjacent the cathode surface, means for producing a magnetic field in-such relation to the path of the holding arc as to confine the holding are cathode spot to a region of the cathode surface which is close to the opening of said passage, and an electrostatic control means arranged in operative relation to the passage.

5. A discharge device comprising an anode, a pool-type cathode, a barrier extending above the cathode surface and defining at least a partial enclosure, a portion of the wall of said enclosure being convergent toward a particular region of the cathode surface, and means for producing a magnetic field in such direction as to impel the cathode spot into the convergent portion of the enclosure, thereby to maintain the spot in a substantially fixed position on the. said particular region of the cathode surface.

6. A discharge device comprising an anode, a pool-type cathode, a V-shaped barrier extending above the cathode surface, and means for producing a magnetic field parallel to the cathode surface and in such direction as to impel the cathode spot into the apex of the said V-shaped barrier.

LAWRENCE D. MILES. 

